Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.68   12.485%   $277.478   $277.48   $277.50   $277.50  
  Purchase #2 $176.73   6.587%   $188.3712   $188.37   $188.35   $188.40  
  Purchase #3 $194.88   6.205%   $206.9723   $206.97   $206.95   $207.00  
  Purchase #4 $197.97   7.572%   $212.9603   $212.96   $212.95   $213.00  
  Purchase #5 $240.87   7.797%   $259.6506   $259.65   $259.65   $259.70  
  Purchase #6 $119.92   12.390%   $134.7781   $134.78   $134.80   $134.80  
  Purchase #7 $213.47   4.755%   $223.6205   $223.62   $223.60   $223.60  
  7 purchase totals = $1,390.52       $1,503.8310   $1,503.83   $1,503.80   $1,504.00